1. Field of the invention
The present invention relates to a dynamic random access memory cell (hereinafter, "DRAM cell") in which a bit line is formed above a charge storage electrode and a method for fabricating the same.
2. Description of the Prior Art
For better understanding of the background of the present invention, there will be described a conventional DRAM cell along with its problems.
Referring to FIG. 1, there is shown a conventional DRAM cell structure in which a bit line is formed above a charge storage electrode. As shown in FIG. 1, a bit line 8 is connected with a drain region 10' after coating an interlayer insulating film 7 on a capacitor of the DRAM cell comprising a plate electrode 6 formed on a dielectric film 5 atop a charge storage electrode 4 of a predetermined size which, in turn, is in contact with a source region 10 of an MOS transistor. The plate electrode 6 must be some distance apart from the bit line 8 because the connection of the capacitor with the bit line causes miss operations.
In this drawing, reference numeral 1 designates a field oxide film, numeral 2 a gate electrode, numeral 2' a gate oxide film, numeral 3 another interlayer insulating film, numeral 11 a P-well and numeral 12 a silicon substrate.
Such conventional DRAM cell structure has to sufficiently overlap with the plate electrode in order to secure sufficient capacitance of the capacitor. However, since some distance between the bit line contact and the plate electrode is indispensable to the fabrication of the DRAM cell so as not to form a short circuit in them, the charge storage electrodes 4 are remote from each other, so that the area of the capacitor cannot help being diminished. Therefore, the capacitance of the capacitor becomes small.
In order to compensate for the small capacitance, there has been made an attempt to make the dielectric of the capacitor thin, or there has been required a three dimensional charge storage electrode. However, methods for the fabrication of such three dimensional structure are very complicated, thereby deteriorating DRAM cell reliability.